The rise in using companion diagnostics to guide selection of pharmacological agents in cancer treatment has led to a need for technologies which can extend these diagnostics to additional patients with difficult to access tumors. Such diagnostic assays are performed on cells extracted from tumors or metastatic cells found distant from the primary tumor site. Evaluation of bodily fluids, including blood, urine, effusions, for disseminated malignant cells originating from the lung, breast or other organs is an alternative to examination of primary tumor tissue, especially when biopsy is not possible at the primary tumor site. For example, pleural effusions, which can be the first presentation of a patient's cancer and thus contain some of the most diagnostically relevant cells, could be used as an easily accessible source of malignant cells to assay specific genetic lesions indicative of susceptibility to targeted therapies. However, the accuracy of these assays is limited by the presence of a large background of normal cells. Current approaches for enriching malignant cells from bodily fluids for these assays can require prior knowledge about the type of malignancy, which is often unavailable, or result in insufficient purity (<40%) for confident diagnoses. Biophysical properties of cells have been shown to be extremely specific label-free biomarkers of malignant phenotypes. Here, we aim to develop an instrument which will isolate target cancer cells using a combination of intrinsic physical biomarkers associated with malignancy - cell size and deformability - with high yield and purity. CytoVale is commercializing a technology, 'deformability cytometry', which assays the biophysical properties of thousands of cells per second and has demonstrated utility in diagnosing malignancy in pleural effusions. Expanding upon its core technology, CytoVale will, in this project, develop an instrument which will be able to isolate malignant cells for companion diagnostic assays, from large volumes of bodily fluids, with higher sensitivity and specificity than currently available techniques. This wil increase the accessibility of these powerful assays which have demonstrated immense clinical success in recent years, thereby improving patient outcomes.